The present invention is related to vacuum sewer systems. More specifically it is related to an arrangement for the supply of atmospheric air to a pneumatic controller of an interface valve, the arrangement preventing water entering the pneumatic controller.
Vacuum sewer systems are an alternative to conventional gravity sewer systems. Vacuum sewer systems are used where conventional systems are expensive due to flat terrain, low housing density, difficult ground conditions, high ground water table, or crossing of water protection areas.
Main components of a vacuum sewer system are:
Collection chambers that are installed in yards or streets and include pneumatic interface valves and controllers; vacuum sewers with systematically arranged high and low points; and a vacuum source, i.e. a vacuum station including vacuum tanks, vacuum pumps and sewage pumps. Fundamentals of vacuum sewer systems are described e.g. in U.S. Pat. No. 3,730,884.
Wastewater flows from houses to the collection chambers. The wastewater is collected in a sump of the collection chamber. A collection chamber also includes an interface valve unit consisting of an interface valve, a pneumatic controller and a sensor pipe. Wastewater that has collected in the sump hydro-statically generates an air pressure in the sensor pipe. This air pressure is transmitted to the controller. The controller opens the interface valve when a certain air pressure is transmitted from the sensor pipe. After wastewater evacuation and drop of sensor pressure, the controller closes the interface valve, but after an additional delay time permitting air admission after wastewater evacuation. The admitted atmospheric air drives the wastewater through the vacuum sewers towards the vacuum station.
A pneumatic controller for a vacuum sewer system was described in U.S. Pat. No. 5,657,784 (The following numerals refer to this U.S. patent). The pneumatic controller 10 includes a three-way valve 20. The three-way valve 20 either transmits vacuum from a vacuum source to the interface valve to open it, or atmospheric pressure from the environment to close it. The controller includes a control chamber 56 that is evacuated through a control valve 22 when the sensor pressure is sufficient to move a sensor diaphragm 16 and open the control valve 22. The control chamber 56 is continuously connected to the atmosphere through an adjustable nozzle 64 and a filter element 68. When the control chamber 56 is evacuated, a control diaphragm 72 is pulled into the control chamber 56 and moves the three-way valve 20 so that it transmits vacuum from the vacuum source to the interface valve thus opening the interface valve. When the wastewater has been evacuated, the sensor pressure drops and the sensor diaphragm 16 returns to its original position. It returns the control valve 22 that shuts the control chamber 56 from the vacuum source. Atmospheric air enters slowly through nozzle 64 into control chamber 56 gradually raising the pressure in the control chamber 56. The control diaphragm 72 and the three-way valve 20 return to their original positions. Atmospheric air is transmitted through the three-way valve 20 to the interface valve and the interface valve is closed. An evacuation cycle is finished.
Atmospheric air can be supplied to the pneumatic controller and the interface valve through an open lid of the collection chamber. However, when the collection chamber is located at a place where surface water could enter the chamber, the chamber cover must be sealed and atmospheric air supplied through a breather line. The breather line can take atmospheric air directly from the environment, e.g. through an external breather tube extending to a level above the maximum flood level, as shown e.g. in U.S. Pat. No. 4,373,838. Alternatively, the breather line can take atmospheric air from the top of the collection chamber sump. The sump is connected to the atmosphere through a vent stack on the gravity drain between the house and the collection chamber. The vent stack also extends to a level above the maximum flood level.
The controller as described in U.S. Pat. No. 5,657,784 has the disadvantage that air bleeds through the controller (The following numerals refer to this U.S. patent). Atmospheric air continuously flows through the controller while the control valve 22 is open. Atmospheric air enters the control chamber 56 through nozzle 64 while air is simultaneously evacuated from the control chamber 56 to the vacuum source. In addition, a direct connection between the atmosphere and the vacuum source is open while the three-way valve 20 switches from one to another position. In the worst case, the controller bleeds for a long time. This happens when the sensor pressure is sufficient to open the control valve 22, but the vacuum strength is insufficient to move the three-way valve 20 and open the interface valve.
Bleeding controllers have the great disadvantage that a large air volume flows through the controllers and their nozzle. When the air is warm and humid, and the controller is cooler than the air, water condensation occurs in the controller. The more air flows through the controller, the more water condenses. Water in pneumatic controllers causes them to fail. The danger of water condensation is particularly great when atmospheric air is taken from the sump because the wastewater in the sump can be warm and the air in the sump becomes warm and humid. Failure of sump breathing controllers is very frequent.
An even greater problem with sump breathing controllers can be caused when wastewater aspiration occurs. When the vacuum strength is insufficient to open the interface valve and evacuate the wastewater, the water level in the sump rises further. When the controller bleeds, the top of the sump is evacuated and the water level can rise until it reaches the sump breather line and is aspirated through the controller.
Entrance of water into the controller must be prevented to guarantee reliable operation of the controller. Water entering a breather line could be condensed water, ground water infiltrating into a leaking breather line or, in the worst case, it could be wastewater from the sump.
A sump breather arrangement was described in U.S. Pat. No. 4,691,731 by Grooms et al. This arrangement was unable to prevent wastewater from entering the controller, as discussed in detail in U.S. Pat. No. 5,570,715 by Featheringill and Grooms.
Another sump breather arrangement was described in U.S. Pat. 5,570,715. The controller is a bleeding controller. When control valve 88 is opened by sensor pressure moving sensor diaphragm 86, atmospheric air is sucked from connection 102 through bores 104 and 106, chamber 79, control valve 88, tubes 120, chamber 82 and connection 96 to the vacuum source. It has the same disadvantage as all other controllers of the prior art that it provides an open connection through the controller between the atmosphere and the vacuum source when the controller is activated by sufficient sensor pressure. Bleeding leads to evacuation of air from the sump into the controller.
To avoid aspiration of wastewater from the sump, the arrangement according to U.S. Pat. No. 5,570,715 also includes a float valve 250 closing the entrance from the sump to the breather line when the wastewater level in the sump rises to a level close to the entrance into the breather line. A problem with this arrangement is that the float valve can be made inoperable by solids or grease floating on the wastewater in the sump. If the float valve does not completely seal the breather line, wastewater enters the controller. Another disadvantage of the arrangement is that the air in the top of the sump is evacuated through the bleeding controller thus further raising the water level in the sump when the vacuum strength is insufficient to open the interface valve. Another problem is that considerable quantities of condensed water could accumulate in the controller during ongoing bleeding.
Main object of the present invention is to improve a pneumatic controller, as described in U.S. Pat. No. 5,657,784, such that entrance of wastewater through a sump breather line is safely prevented. The improved controller should non-bleeding under all circumstances. The controller should have no open connection through the controller between the breather line and the vacuum source. The improved controller should be capable to be connected to an open sump breather line without the danger that wastewater from the sump enters the controller, and without the need for a float valve in the sump.
The improved controller should need a very small volume of breather air for operation in order to reduce the danger of condensation, whether it is connected to a sump breather or an external breather line.
The improved controller should also be compact, easy to manufacture, reliable and inexpensive.
Another object of the present invention is to provide an arrangement within a breather line for the collection and removal of water, such as condensed water, infiltration water or wastewater, from the breather line thus preventing water from being conveyed through the breather line to the controller. This arrangement should be reliable, simple and inexpensive.
The main object of the invention is achieved by an improved controller including means preventing, under all conditions and circumstances, an open connection from the breather line through the controller to the vacuum source. The means preventing such bleeding include a control valve either closing a connection between a control chamber and the breather line or closing a connection between the control chamber and the vacuum source, but under no circumstances opening a connection between the breather line and the vacuum source.
More specifically, the improved controller includes in a single body a control valve, a control chamber, a control diaphragm and a three-way valve, the control chamber having connections to the vacuum source and to the atmosphere, but either shutting the connection to the vacuum source or the connection to the atmosphere. The control chamber is either evacuated (when the controller is activated by sufficient sensor pressure) or aerated (after wastewater has been evacuated and the sensor pressure has dropped), but simultaneous flow of air in and out of the control chamber cannot occur.
Only a small volume of air flows through the breather line during an evacuation cycle to the controller and interface. The air volume flowing into the control chamber is only a fraction of the volume of control chamber, the fraction depending on the vacuum strength. The air volume flowing to the interface valve is a fraction of the volume of the actuator of the interface valve. These volumes are only a very small fraction of the volume of air that is entrapped in the top of a sealed sump. The wastewater level in the sump rises only by a marginal amount and cannot reach the breather line. Entrance of wastewater into the breather line is thus prevented. The volume of water that could be condensed in the controller is greatly reduced.
Air from the sump does not enter the control chamber before the wastewater has been evacuated. Then the wastewater level in the sump has dropped and fresh atmospheric air has entered the sump. This fresh atmospheric air is less warm and humid than the air that had been in the top of the sump before the wastewater was evacuated.
A latching means is also included in the controller. This latching means can be a magnet attached to the controller body and a steel plate attached to the control diaphragm, or vice versa. A certain vacuum strength in the control chamber that is required for proper evacuation of wastewater from the sump is necessary to overcome the latching force and move the control diaphragm into the control chamber. The latching means could also be mechanical mechanisms, such as a spring loaded catch element.
Open pressure communication between the sump and the control diaphragm has an important advantage. When rising wastewater in the sump compresses the air that is entrapped in the top of the sump, an increased pressure (above atmospheric pressure) is transmitted to the control diaphragm exerting an increased force pushing the diaphragm into the control chamber. As a result, this increased pressure helps the vacuum pressure in the control chamber to overcome the latching force. A smaller vacuum strength is sufficient to pull the diaphragm into the control chamber and thus switching the three-way valve and opening the interface valve. The interface valve is thus opened at a reduced vacuum strength. The vacuum strength required for proper evacuation of the wastewater from the sump is also reduced because the elevated water level in the sump adds an increased hydrostatic pushing force to the pulling vacuum force from the vacuum source. Operability of the vacuum sewer system is thus improved.
An adjustable nozzle is provided in a connection between the breather line and the control chamber. The air flow through the breather line into the control chamber is restricted by the nozzle thus slowing the rise of the pressure in the control chamber. Closing of the interface valve is thus adjustably delayed permitting air evacuation through the sump after wastewater evacuation. The ratio of the air/wastewater volumes can be increased by reducing the orifice of the nozzle.
The nozzle is protected by a filter element that is provided between the breather line and the nozzle. This filter element retains dirt that could clog the small nozzle orifice.
According to the present invention, the other object is achieved by providing an arrangement preventing entrance of water into a pneumatic controller of an interface valve through a breather line including:
A first chamber having a bottom, a cover and a wall, a first connection to the breather line for intake of atmospheric air, a second connection to the controller for transmitting atmospheric air to the controller, and a third connection to a vacuum source; and a float body within the first chamber arranged such that the float body is closing and sealing the third connection while few water has collected in the first chamber, and is opening the third connection as a result of a buoyancy force acting on the float body when more water has collected in the first chamber.
In other words, the first chamber is arranged in a breather line and water entering the breather line or being condensed within the breather line is separated and collected in the chamber. As long as no or little water is collected, the breather connection is open between the atmosphere and the controller. While water is collected in the first chamber, the water raises a float body thus opening the third connection through which collected water is sucked into the vacuum sewer system. The water level in the third chamber is thus limited and can never reach the second connection to the controller. After the water has been evacuated the float body is sucked towards the third connection thus closing it. The third chamber acts as a water trap that is automatically evacuated.
As an additional feature, the float body closes and seals the second connection when the float body is further lifted by buoyancy force, whereby the float body first opens the third connection, and thereafter closes the second connection, as the float body is lifted. This is to provide an additional safety against water entering the controller through the second connection. This additional safety could be needed for the case that the strength of the vacuum source would be insufficient for fast evacuation of the chamber, e.g. due to a failure of the vacuum system, or if more water would enter the chamber than can be evacuated from the chamber.
The first connection to the atmosphere is preferably located in the wall near the cover so that the float body cannot close the connection to the atmosphere. In this way it is guaranteed that the water is rapidly driven through the third connection by the difference between atmospheric pressure and vacuum pressure. In addition it is guaranteed that water is driven from the breather line into the chamber. This is particularly important if the breather line has a low point that could become water logged thus reducing the pressure that is transmitted to the controller.
The first chamber has preferably a fourth connection to the interface valve transmitting atmospheric pressure to the interface valve. A typical interface valve has two connections, one connection transmitting vacuum or atmospheric pressure from the controller into the interface valve""s actuation volume, e.g. a bellow, the other connection transmitting atmospheric pressure as reference pressure to a volume in the valve casing. While the float body can close the second connection to the controller, the fourth connection remains always open to guarantee that the interface valve can be closed at any time. Preferably the fourth connection is, like the first connection, penetrating the wall of the chamber near its cover so that it is always open, but cannot be reached by the water level.
Alternatively, the second connection could be connected to the controller and the interface valve, i.e. a tube to the interface valve branches off from a tube between the first chamber and the controller.
The third connection is provided with a peripheral seal, such as a lip seal. Sealing is supported by vacuum force pulling the float body towards the third connection and against the seal.
While it would be obvious to locate the third connection at the bottom of the first chamber, it is unexpectedly better if the third connection penetrates the wall of the chamber. A much smaller buoyancy force is required to open the third connection because the gravity of the float body and the suction force exerted on the float body from the third connection have an angle of approximately 90 degrees. The third connection is thus opened when a relatively small volume of wastewater has collected. The volumes of the float body and of the third chamber can be kept small.
It is further proposed to provide the first chamber with a sloped bottom, sloped towards the third connection. After water has been evacuated from the first chamber, the float body is driven by its gravity towards the third connection. It slides or rolls on the bottom towards the third connection until it closes and seals the third connection.
The float body is preferably a sphere with a diameter D. The sphere rolls on a sloped bottom of the first chamber towards the third connection and is sucked towards the third connection so that it seals the third connection.
The first chamber has preferably a cylindrical shape. Its height should be less than 2*D and its internal diameter smaller than 1.5*D. The distances of the first and fourth connections from the cover of the first chamber should be smaller than 0.5*D so that these connections cannot be closed by the floating sphere.
As a further improvement of the arrangement according to the invention it is proposed to provide a second chamber with a bottom, wall and cover. The second chamber is connected with the first chamber through the third connection, to the controller through a fifth connection, and to the vacuum source through a sixth connection. The sixth connection should be located at the bottom of the second chamber so that water drains through the sixth connection towards the vacuum source. Vacuum pressure is transmitted through the second chamber to the controller and to the third connection of the first chamber. The second chamber serves as a surge volume preventing wastewater from entering the fifth connection to the controller. Wastewater could be driven through the sixth connection by a pressure surge in the vacuum system. The controller is supplied with vacuum through the fifth connection, or in other words, air is evacuated from the controller through the fifth connection. The fifth connection is preferably penetrating the wall of the second chamber near its cover in order to prevent water from entering the fifth connection. As an additional safety means a check valve can be installed in a conduit between the sixth connection and the vacuum source. This check valve would prevent the pressure surge and wastewater from entering the second chamber while permitting air and water to be evacuated from the second chamber to the vacuum source.
The first and the second chamber can be located in a single housing such that the bottom of the first chamber is the cover of the second chamber. The housing and both chambers preferably have a cylindrical shape. The housing can be made inexpensively of a PVC pipe, forming the walls of both chambers, and of PVC caps forming the cover of the first chamber and the bottom of the second chamber. The pipe could be transparent. The bottom of the first chamber and the cover of the second chamber can be formed by a circular or elliptical plate separating the chambers. While the upper cap should be removable to permit removal of the float body, the lower cap can be fixed to the pipe, e.g. by solvent welding. An O-ring in a groove of the upper cap seals the spacing between the cap and the pipe.
The volume of the first chamber should be larger than the volume of air entering through the breather line during an evacuation cycle. The air rests in the first chamber and vapor can be condensed before the air enters the controller. This is particularly beneficial when the valve chamber is cooler than the atmospheric air entering the first chamber through the breather line.